mediawiki.htmlform: Use auto width for Chosen selects

Upgrading jQuery Chosen to 0.9.14 (which adds a "width" option) and
setting width: auto in chosen calls for HTMLForm elements.

Change-Id: Ib87f00ae0f3ad960d35d7a3c4529e56bbdaa6c38
Merge "mediawiki.htmlform: Use auto width for Chosen selects"